joining me now is former fbi profiler, clint van zandt. clint, thanks for being here. >> good to be with you, al. >> what kind of information can we learn from photos like this? >> well, one of the things that the fbi will do is they'll take photographs of the actual blast area. they'll superimpose it over a photograph like you just showed us to try to suggest, did that blast actually originate from that bag or was it left, right or behind it? so we've got -- we've got a baseline of where the explosion took place. any other photographs will be compared against those two explosion sites, number one, to see if a bag had been there. number two, we'll be looking for someone who carried such a bag. remember, al, that the fbi describes two different black nylon bags. if you think about -- if you think about these pressure cookers, a friend of mine, larry johnson, former cia, commented that these would weigh about 20 pounds each. that's a lot of weight for somebody to carry in that area, al. >> now, what kind of damage can these type of bombs do,